The present invention concerns a circuit for controlling the speed of a magnetic tape reel motor of an audio recording/playing mechanism and method therefor.
Generally, a data recording/playing mechanism using a magnetic reel tape controls the running speed of the tape reel by using the capstan motor. When the tape runs at a high speed as in fast forwarding or rewinding, the capstan motor is not proper to use and a reel is used, instead. Meanwhile, the mechanism for recording/playing digital data on/from a digital audio tape (DAT) by using a rotational head should read precisely the data recorded on the tape running at a high speed so as to perform high speed search. To this end, the relative speed between the tape running speed and the peripheral speed of the rotational head must be constant both at the normal and high tape speeds.
Further, the tape must run at a constant high speed, so that the reliability of retrieving data from the tape is increased, and the peripheral speed of the rotational head is easily controlled to maintain a constant relative speed. However, to control the tape running speed through control of the reel, it must be first considered that the amount of the tape wound around the reel is continuously changing, and thus the tape running distance per reel revolution is also varying continuously. Hence, the speed of the reel revolution must be continuously changed to keep the tape running speed constant. To this end, the conventional reel control method changes the reel revolution speed so as to make constant the sum of the revolution periods of the supply and take-up reels. In this case, the reel tape running speed varies as shown in FIG. 2 (See the curve 23), so that the data retrieval reliability is worsened at the high speed than at the normal speed [See FIG. 2 (21)] and control of the drum revolution speed for keeping the constant relative speed becomes difficult.